Deformed Intersecting D6-Brane GUTS I

TL;DR

This paper constructs four-stack intersecting D6-brane models in type IIA string theory that replicate the Standard Model with three generations, no extra matter, and realistic phenomenology, including proton stability and neutrino masses.

Contribution

It introduces a new class of four-stack string GUT models based on intersecting D6-branes that achieve realistic Standard Model features without extra matter or gauge groups.

Findings

Models contain exactly three generations of Standard Model particles.

Proton remains stable with no dangerous color triplet couplings.

Neutrino masses and GUT scale mass relations are successfully realized.

Abstract

By employing D6-branes intersecting at angles in $D = 4$ type IIA strings, we construct {\em four stack string GUT models} (PS-I class), that contain at low energy {\em exactly the three generation Standard model} with no extra matter and/or extra gauge group factors. These classes of models are based on the Pati-Salam (PS) gauge group $SU(4)_C \times SU(2)_L \times SU(2)_R$. They represent deformations around the quark and lepton basic intersection number structure. The models possess the same phenomenological characteristics of some recently discussed examples (PS-A class) of four stack PS GUTS. Namely, there are no colour triplet couplings to mediate proton decay and proton is stable as baryon number is a gauged symmetry. Neutrinos get masses of the correct sizes. Also the mass relation $m_e = m_d$ at the GUT scale is recovered. Moreover, we clarify the novel role of {\em extra} branes, the latter having non-trivial intersection numbers with quarks and leptons and creating scalar singlets, needed for the satisfaction of RR tadpole cancellation conditions. The presence of N=1 supersymmetry in sectors involving the {\em extra} branes is equivalent to the, model dependent, orthogonality conditions of the U(1)'s surviving massless the generalized Green-Schwarz mechanism. The use of {\em extra} branes creates mass couplings that predict the appearance of light fermion doublets up to the scale of electroweak scale symmetry breaking.